1. Field of the Invention
The present invention relates to an arc welding method using an industrial robot.
2. Description of the Related Art
In arc welding using an industrial robot, arc welding is performed while relatively moving a welding torch and a workpiece along a taught welding line. In some cases, the arc welding is performed by fixing the welding torch and by moving the workpiece. In general, however, the welding torch is mounted to a wrist at a distal end of a robot arm, and arc welding is performed by operating the robot with respect to the fixed workpiece so that the welding torch is moved along the taught welding line. However, there has been a problem such that, at the start of welding, a hole is apt to be made in the workpiece due to excessive heating of the workpiece before the robot is accelerated (before a speed of the welding torch relative to the workpiece is accelerated). Since the welding heat is concentrated on an end portion of the welding line in the case where the end portion is identical with an end portion of the workpiece, it is necessary to reduce a welding condition so as to weld at a lower welding speed.
In TIG (Tungsten Inert Gas) arc welding for aluminum which is a heat-sensitive material, the temperature of the workpiece progressively rises during welding so that a welding speed must gradually be raised in accordance with the rise of temperature of the workpiece. In welding the entire periphery of a workpiece with a small diameter, it is necessary to increase a final welding speed two to three times the initial welding speed. Besides, other welding conditions (current, and voltage) must also be varied gradually in accordance with the variation of the welding speed.
Thus, in the prior art, there has been employed a method, in which, for the purpose of varying welding conditions, auxiliary points are taught to specify the welding speed, voltage and current between the teaching points, thereby gradually increasing or decreasing the welding conditions such as welding speed, voltage, and electric current. In this case, a trial and error method is employed to determine a section between the auxiliary teaching points, and the welding conditions within the section, such as welding speed, voltage and current.
For example, in practice, even in the case of a linear weld line, when starting welding, a plurality of auxiliary teaching points are given between a welding start position and a position on the weld line, spaced out by a predetermined amount, and progressively increasing welding speed, voltage and current are taught between the respective points. Further, in practice, if an end portion of a weld line is identical with an end portion of a workpiece, the auxiliary teaching points are given to divide a range from a position set by a predetermined amount ahead of the end portion of the weld line to the end portion into a plurality of sections, and progressively decreasing welding speed, voltage and current are taught between the respective points.
As stated above, in the conventional method, a large number of auxiliary teaching points must be taught for the purpose of varying welding conditions such as welding speed, voltage and current. Furthermore, it is necessary to individually teach each of the welding conditions between the teaching points. Besides, since the trial and error method is employed to determine the section between the auxiliary points, welding speed, voltage and current value, the teaching processes are very complicated and difficult, resulting in a heavy burden on a teaching operator.